It is a fairly accepted truism that communications is the lifeblood of business. As domestic and international businesses continue to expand at an extraordinary pace, these businesses become increasingly reliant upon telecommunications services to remain competitive in a global marketplace. Whether it is talking to a customer over the Public Switched Telephone Network (PSTN), sending an electronic mail message over the Internet, or trading product specifications over a local area network, disruptions to a communications network can mean significant losses to a business. Extended outages are particularly harmful, but even brief outages can be bothersome. The result is ever increasing demands by telecommunications customers for a virtually uninterruptible network.
One element to creating a virtually uninterruptible network is to correct network outages as rapidly as they occur. At a very high level a network can be viewed as a pattern of communications nodes interconnected by communications links. The communications nodes can include electronic or optical cross-connects ("switches"), personal computers, servers, printers, or any other type of network device. The communications links include some type of media for transporting communications signals, such as optical fiber, twisted-pair copper wires, co-axial cable, radio frequencies, and so forth. An example of a communications network would be a set of communications switches ("switching fabric") connected together by optical fibers ("optical links"). If an optical link is damaged, as frequently occurs such as when a construction company digs in the area where the optical link is buried, the communications signals carried by the optical link must be quickly re-routed. This is also true if a switching fabric becomes inoperable, although the problem of re-routing the communications signals becomes an even greater challenge in this case.
Several conventional techniques have been developed to restore communications in the event of a link or node failure on a network. These techniques are loosely referred to as "network restoration techniques," and in most cases refer to an algorithm for re-routing the communications signals carried by the failed link, or switched by the inoperative node. For example, a class of algorithms have been developed that are referred to as "flooding algorithms." Communication messages for service restoration in case of a failure in the network are transmitted through links between the switches. The switches then electronically process these messages to take appropriate action to restore the failed traffic in the event of, for example, a link failure.
There are basically two types of flooding algorithms for restoring the failed traffic in the event of a link failure. The first is referred to as "link based restoration," while the second is referred to as "path-based restoration. Path based restoration attempts to re-route failed circuits between the originating node and destination node of the individual circuits in the failed link. By way of contrast, link based restoration attempts to re-route all traffic around the failed link regardless of the origination and destination of the bearer traffic on the failed link.
Link based restoration and path based restoration each have their advantages and disadvantages. For example, link based restoration is typically faster than path based restoration, but is less efficient in terms of restoration capacity utilization. Conversely, path based restoration is slower than link based restoration, but utilizes restoration resources more efficiently since the origination and destination nodes of the failed nodes are typically distributed throughout the system.
These techniques, however, are unsatisfactory for a number of reasons. For example, a completely optical layer network above the Synchronous Optical Network (SONET) layer is fast becoming a reality. The optical network is being driven both by the commercial availability of dense wavelength division multiplex (DWDM) technology and the continuing growth of traffic. Current DWDM systems are offering sixteen or more OC-48 channels on a pair of fibers. In the future it may grow to more than one hundred wavelengths, and the channel capacity may increase to at least 10 Gigabytes per second (Gbps). When a substantial number of links are deployed in the network, it will be necessary to manage the network at the optical layer. This management will require the capability to restore the network in the optical layer. Networking and restoration at the optical layer is highly desirable for optical switching systems. No signal will undergo optical to electrical conversion at these optical cross-connect systems. Therefore, restoration from a failure in the network will either require communication and processing messages between the optical cross-connect systems in the optical domain or an auxiliary optical channel which will undergo optical to electrical conversion and processing just for messaging. It is desirable to eliminate the need of an auxiliary channel for the purpose of restoration. Even if it is required for other purposes, it is extremely important that the processing required at each node remains simple for implementing a fast restoration technique in an optical network. Conventional network restoration techniques fail to address any of these concerns, and are not designed to perform network restoration in the optical domain.
In view of the foregoing, it can be appreciated that a substantial needs exists for a method and apparatus for providing fast restoration from a link or a node failure in a network, that solves the above-discussed problems.